Large-volume application of high-brightness LED elements (LED: Light emitting diode) is well established for signaling and signage. High-brightness LEDs are expected to replace conventional lamps in lighting applications within a few years.
High-brightness LEDs have been developed using GaN based materials. It is known that the optical and electrical properties of such LEDs may show a large variation. Output (radiative) flux, wavelength, forward voltage and resistivity may show a spread. In particular, the variation in these properties results in variation of the output flux from one LED to another for a given driving current.
EP 0 702 347 A1 discloses a dot-matrix LED display which has a data storage unit for storing brightness-corrected data prepared according to the characteristic brightness of each of the LEDs to minimize brightness difference among the LEDs.
US 2006/186819 A1 discloses a manufacturing process for storing measured light output internal to an individual LED assembly, and an LED assembly realized by the process. The process utilizes a manufacturing test system to hold an LED light assembly a controlled distance and angle from the spectral output measurement tool. Spectral coordinates, forward voltage, and environmental measurements for the as manufactured assembly are measured for each base color LED. The measurements are recorded to a storage device internal to the LED assembly. Those stored measurements can then be utilized in usage of the LED assembly to provide accurate and precise control of the light output by the LED assembly.
Furthermore, it is known to measure properties of LEDs after manufacturing, and classify the LEDs based on the results. The classification into classes or binnings is typically done based on output flux, wavelength and forward voltage of the LEDs.
Classified LEDs are then shipped to manufacturers of lighting applications.
Based on the binning information, LEDs can be selected, grouped and tuned for lighting applications. However, manufacturers of such lighting applications still encounter some obstacles: the logistics of selecting LEDs are extensive and complex and adversely affect achieving a reproducible temperature color of LEDs from one product of the lighting application to another.